The invention concerns a metering device for fine grain powder, in particular for medicinal powder for pulmonary administration, as well as a method for operating such metering device.
As a result of the rise in asthma and COPD (chronic obstructive pulmonary disease), administration forms by inhalation of medicines for therapy of these diseases are becoming more and more important. The pulmonary administration—in addition to injection or infusion—is also an alternative for numerous medicines that cannot be applied per orally because the substances would be destroyed in the gastro-intestinal tract or would have an unsatisfactory bioavailability. In this connection, powders for inhalation have in comparison to solutions for aerosol administration the advantage of improved active ingredient stability but are more difficult to process because all active ingredient particles must have a size of <5 μm in order to reach the target location, i.e., alveoli. Powder inhalers with individually packaged doses are preferred because of their better stability and higher metering precision.
Smallest quantities of such powders that, for medical applications, are in the range of 0.2 mg to 50 mg, must be metered very precisely and filled into the target vessel. As a result of the small particle size these powders agglomerate greatly wherein the mass of individual agglomerates may be greater than the permissible metering tolerance. This results in the lack of metering precision in conventional volume-based metering. When these agglomerates upon metering and inhaling remain intact, the active ingredient can reach only to a limited extent the alveoli. The aim is therefore to dissolve these agglomerates during the metering process, to fill in the powder as finely divided as possible into the target container, and to achieve in this connection a high metering precision.
U.S. Pat. No. 4,472,091 discloses a metering device for fine grain dry powder in which the powder is stored in a closed funnel-shaped supply container. The funnel-shaped supply container has at its bottom side an opening that is closed off by means of the discharge valve. The valve body of the discharge valve is axially moveable by means of piezoelements and, in this way, can be opened, closed, and also caused to vibrate. Into the supply container and also into an intermediate space arranged below, an air passage opens, respectively, in order to generate a powder-air mixture which is then passed through the discharge valve into the target container. The vibration movement of the valve body contributes to loosening of the powder and to an improved discharge from the supply container.
A disadvantage in this connection is that breaking up of the agglomerates in the powder cannot be ensured in a reliable fashion. In particular, a complex sensor system and a corresponding process control are required in order to maintain a satisfactory filling level of the powder in the supply container. When dropping below the minimally required filling level, the container must be opened and refilled which impairs the economic efficiency of the arrangement. The arrangement is complex with respect to its configuration. The piezoelectric drive of the valve body is positioned within the powder stream and therefore must be protected with respect to soiling and to prevent contamination of the powder.
The invention has therefore the object to provide a metering device for fine grain powder that, while of a simple configuration and minimal operating expenditure, provides a precise and economic metering of the powder.